The present invention is related generally to the field of orthodontics, and more particularly to a system and a method for gradually repositioning teeth.
A fundamental objective in orthodontics is to realign a patient""s teeth to positions where the teeth function optimally and aesthetically. Typically, appliances such as braces are applied to the teeth of the patient by a treating orthodontist. Each appliance exerts continual forces on the teeth which gradually urge the teeth toward their ideal positions. Over a period of time, the orthodontist adjusts the appliances to move the teeth toward their final destination.
The process of attaching the braces to teeth is tedious and painful. Additionally, each visit to the orthodontist is time consuming and expensive. The process is further complicated by uncertainties in determining a final arrangement for each tooth. Generally, the final tooth arrangement is determined by the treating orthodontist who writes a prescription. Traditionally, the prescription is based on the orthodontist""s knowledge and expertise in selecting the intended final position of each tooth and without a precise calculation of forces being exerted on the teeth when they contact each other.
The invention provides a method for fitting a set of upper and lower teeth in a masticatory system of a patient. The method generates a computer representation of the masticatory system of the patient; and determines an occlusion from the computer representation of the masticatory system.
Implementations of the invention include one or more of the following. The occlusion may be a static occlusion, which is determined by modeling an ideal set of teeth; automatically applying the ideal set of teeth to the computer representation of the masticatory system of the patient; and optimizing the position of the patient""s teeth to fit the ideal set of teeth. The modeling step may select one or more arch forms specifying the ideal set of teeth. The applying step may include registering a model of the upper and lower teeth with a model of the masticatory system; simulating the motion of the jaws to generate contact data between the upper and lower teeth; and placing the tooth in a final position based on the contact data. The model may be registered using X-ray data, computed tomography data, or data associated with a mechanical model. The simulating step may apply kinematics to the model of the teeth or a constrained motion to the model of the tooth. The placing step may be based on a measure of undesirability to the contacts. The position of the tooth may be determined according to the measure of undesirability, such as by minimizing the measure of undesirability. The measure of undesirability may be a function of one or more of Peer Assessment Rating (PAR) metrics, distance-based metrics and shape-based metrics. The simulating step may provide a library of motions with protrusive motions, lateral motions, or tooth-guided motions. Physical forces may be applied to the patient""s jaws. The computer representation of the masticatory system may be updated with new patient data. The new patient data may be used with the old data in applying a final position transform to the second teeth model. The matching step may compare correspondences between the first and second teeth models. The correspondences include feature correspondences. The final position transform may include information from a new prescription.
Other implementations include one or more of the following. The occlusion determining step includes determining one or more indices based on the tooth position; determining an optimality index from the indices; and setting the tooth according to the optimality index. The optimality determining step includes minimizing the optimality index. The indices may be based on a Peer Assessment Rating (PAR) index, a distance metric, or a shape metric. The shape metric may be derived from an arch. The indices may be based on an occlusional index or an orthodontic index. The setting of the teeth may be based on a correspondence of tooth features, including a correspondence of tooth cusps, tooth fossae, or tooth ridges. The optimality index may be optimized using one of simulated annealing technique, hill climbing technique, best-first technique and heuristics technique. The implementation may determine whether a tooth movement reduces the index. The tooth movement may be made along each major axis and may include rotations. The tooth position may be updated if the tooth movement reduces the index.
In a second aspect, a computer-implemented apparatus defines a fit between a set of upper and lower teeth in a masticatory system of a patient. The apparatus comprises instructions operable to cause a programmable processor to generate a computer representation of the masticatory system of the patient; and determining an occlusion from the computer representation of the masticatory system.
Implementations of this aspect include one or more of the following. The invention may determine a static occlusion through instructions to model an ideal set of teeth; automatically apply the ideal set of teeth to the computer representation of the masticatory system of the patient; and optimize the position of the patient""s teeth to fit the ideal set of teeth. The occlusion determining instruction may also include instructions to: determine one or more indices based on the tooth position; determine an optimality index from the indices; and set the tooth according to the optimality index.
In another aspect, a system for defining a fit between a set of upper and lower teeth in a masticatory system of a patient includes a processor; a display device coupled to the processor; and a data storage device coupled to the processor, the data storage device storing instructions operable to cause the processor to generate a computer representation of the masticatory system of the patient and determine an occlusion from the computer representation of the masticatory system.
In another aspect, a system for generating one or more appliances for a patient includes a processor; a display device coupled to the processor; a data storage device coupled to the processor; a scanner coupled to the processor for providing data to model the masticatory system; means for defining a fit between a set of upper and lower teeth in a masticatory system of the patient; and a dental appliance fabrication machine coupled to the processor for generating the appliances in accordance with the fit of the teeth.
Advantages of the invention include one or more of the following. When a prescription or other final designation is provided, a computer model can be generated and manipulated to match the prescription. The prescription may be automatically interpreted in order to generate an image as well as a digital data set representing the final tooth arrangement.